Gas treatment apparatus are known. Such apparatus are used for treatment of effluent gases arising from epitaxial deposition processes. Epitaxial deposition processes are increasingly used for the manufacturing of high-speed semiconductor devices, both for silicon and compound semiconductor applications. An epitaxial layer is a carefully grown, single crystal silicon film. Epitaxial deposition utilizes a silicon source gas, typically silane or one of the chlorosilane compounds, such as trichlorosilane or dichlorosilane, in a hydrogen atmosphere at high temperature, typically around 800-1100° C., and under a vacuum condition. Epitaxial deposition processes are often doped with small amounts of boron, phosphorus, arsenic, germanium or carbon, as required, for the device being fabricated. Etching gases supplied to a process chamber may include halocompounds such as HCl, HBr, BCl3, Cl2 and Br2, and combinations thereof. Hydrogen chloride (HCl) or another halocompound, such as SF6 or NF3, may be used to clean the chamber between process runs.
In such processes, only a small proportion of the gas supplied to the process chamber is consumed within the chamber, and so a high proportion of the gas supplied to the chamber is exhausted from the chamber, together with solid and gaseous by-products from the process occurring within the chamber. A process tool typically has a plurality of process chambers, each of which may be at respective different stage in a deposition, etching or cleaning process. Therefore, during processing a waste effluent stream formed from a combination of the gases exhausted from the chambers may have various different compositions.
Before the waste stream is vented into the atmosphere, it is treated to remove selected gases and solid particles therefrom. Acid gases such as HF and HCl are commonly removed from a gas stream using a packed tower scrubber, in which the acid gases are taken into solution by a scrubbing liquid flowing through the scrubber. Silane is pyrophoric, and so before the waste stream is conveyed through the scrubber it is common practice for the waste stream to be conveyed through a thermal incinerator to react silane or other pyrophoric gas present within the waste stream with air. Any perfluorocompounds such as NF3 may also be converted into HF within the incinerator.
When silane burns, large amounts of silica (SiO2) particles are generated. Whilst many of these particles may be taken into suspension by the scrubbing liquid within the packed tower scrubber, it has been observed that the capture of relatively smaller particles (for example, having a size less than 1 micron) by the scrubbing liquid is relatively poor. In view of this, it is known to provide an electrostatic precipitator downstream from the scrubber to remove these smaller particles from the waste stream.
Although such apparatus provide for treatment of the effluent gas stream, they have a number of shortcomings. Accordingly, it is desired to provide an improved gas treatment apparatus.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.